In the quest for high efficiency emissions-free internal combustion engines, engine manufacturers have attempted to develop engine fuel supply systems that achieve complete fuel combustion. While this goal has thus far proved somewhat illusory, significant improvements in both combustion efficiency and emissions reduction have occurred. Simple, reliable engine fuel systems of reasonable cost which will achieve the aforesaid goals are still being sought, however.
A major purpose in seeking complete fuel combustion is to reduce polluting engine emissions, especially in the levels of hydrocarbons, nitrogen oxides and particulate materials. Fuel injectors, in particular, have been designed purporting to achieve efficiency of combustion, fuel economy and emissions abatement. Injectors such as those described in U.S. Pat. Nos. 3,951,117, 4,463,901, and 4,621,605, assigned to the same assignee as the present invention, have proven to be effective, reliable and economical. However, the achievement of proposed further restrictions on levels of hydrocarbons, nitrogen oxides and particulates in vehicle emissions could present problems, even with injectors such as these. The cost effectiveness and fuel economy associated with currently available fuel injectors is likely to be sacrificed, especially if after treatments such as catalysts are required to achieve acceptable levels of these pollutants. Not only can after treatments be costly, they also can present substantial maintenance problems.
Therefore, dealing with pollutants at the source--in the combustion space--presents a simpler, more efficient, cost effective solution. This means increasing the efficiency of the combustion process which, in turn, requires the injection of fuel at high pressures, considerably higher pressures than have heretofore been attained, particularly during low speed engine operation. The injection pressure capabilities of previously available fuel injectors has been limited to SAC pressures (pressure of the fuel in the injection chamber just in front of the injector spray holes) to under 20,000 psi.
In order for each of the engine injectors to be able to sustain SAC pressures substantially above 20,000 psi, however, the engine fuel supply system must be able to provide precisely controlled amounts of fuel and timing fluid to each injector at the precise time required in the injection cycle. The fuel supply systems described in U.S. Pat. Nos. 3,951,117; 4,463,901 and 4,621,605 are designed to supply fuel and timing fluid to injectors in which SAC pressures are limited to less than 20,000 psi, even under high speed engine operating conditions. While these fuel supply systems adequately meet the needs of such fuel injectors, they are not sufficiently responsive to engine operating conditions to supply the needs of very high pressure injectors. Moreover, these fuel supply systems are not designed to cooperate with fuel injectors that must pressurize the fuel to a substantial level in the low speed operating range without increasing the injection pressure more than necessary in the high speed operation range. Further, they are not sufficiently sensitive to the wide range of engine operating parameters required for the efficient operation of high pressure injectors, nor do they provide the degree of precise independent control of timing pressures needed.
Many of the fuel supply systems currently available, moreover, are made up of components such as pumps, pressure regulators and fuel lines that are mounted externally of the engine head thereby increasing the risk of fuel leakage, and further complicating maintenance and other problems associated with fuel plumbing external to the engine head.
Consequently, there is a need for a fuel supply system capable of responding precisely to a wide range of engine operating parameters to provide the precise supply of both fuel and timing fluid to each engine fuel injector required to enable each injector to achieve SAC pressures in excess of 30,000 psi during injection. There is a further need for such a fuel supply system including components that may be integrally mounted with the engine cylinder head in locations that will enhance the efficient operation of these components.